Yesterday I put up a list of the rules I need to add to the DFRPG for DF Felltower.
The Critical Hit rules I mentioned are the ones from Basic Set: Characters, p. 326.
They are under Attacking, the last two paragraphs of Attack Roll. The short version is that a 3 is maximum damage, a 4-whatever your critical hit number is (4, 5, 6, even 7+ for certain Swashbucklers) just hits without allowing a defense roll.
And that's is.
We use the Critical Miss Tables. But in the interest of speed, we skip the Critical Hit Tables. It's been fine, and has in fact sped things up without anyone really feeling like they've lost out.